That’s a smart question to ask; many design engineers overestimate how accurate traditional motors and actuators stay over long travel runs, mistakenly believing that if the solution works well for short runs, it will work equally well on long ones. Although many types of linear systems can meet two of your three requirements (long travel lengths, high speed and high positioning accuracy), linear motor actuators are the only type that can provide all three without compromise. They are often used in semiconductor manufacturing, consumer electronics inspection, medical and life science applications, machine tools, printing and packaging applications.
To provide a little background, let’s define linear motors. Essentially, a linear motor is a rotary motor that has been unwound and laid out flat. It allows coupling the motor directly to the linear load; in contrast, other designs use a rotary motor and couple through mechanics, which can introduce backlash, efficiency losses and other inaccuracies. Linear motors tend to have higher maximum velocities compared to ball screws of the same travel length as well.
Three main types of linear motors are used in today’s marketplace. Depending on the specific application, a wide range of solutions is available in any of these three motor types.
The first is ironcore, which has coils wound around teeth made of ferrous material, wrapped in laminate. These motors have the highest force per size, good heat transfer, and are generally the least expensive. However, the iron in the motor leads to increased cogging (torque due to interactions of the magnets in the motor), so they are often somewhat less precise than the second type, ironless linear motors.
As the name implies, an ironless linear motor doesn’t have any iron inside. The forcer is essentially a plate made of epoxy in which the tightly wounded copper coils are inserted. The forcer slides in between a double row of magnets that face each other. The magnets are linked on one side by a spacer. This is also known as a U-channel magnetic way. The main advantage of ironless motors is a reduction in attractive forces and the elimination of cogging that the iron in a motor would normally cause. This makes them more precise than the ironcore. However, the two rows of magnets make ironless units more expensive than the ironcore. Managing heat transfer can also be difficult, so it’s important to understand early whether a particular application will run the risk of overheating. The newest ironless motor design features coils that are overlapped, providing more surface contact for heat dissipation. This design also allows the motor to have a higher force density.
The third and final type is a slotless linear motor, which is basically a hybrid of the first two types. A slotless motor has a single row of magnets like the ironcore, which helps keep its price lower. A laminated backiron ensures good heat transfer, as well as lower attractive forces and cogging than an ironcore motor. Slotless motors also offer the advantage of a lower height profile than ironless in addition to their lower price is a lower height profile. For designers who prioritize keeping the components within their machines as small as possible, every millimeter of space saved can be crucial.
